COVID-19: No new cases as South Australia enters the first day of extreme lockdown restrictions

South Australia has recorded no new COVID-19 cases - good news as the state begins six days of extreme lockdown restrictions.

Bars, restaurants, schools and universities have all been shut in an attempt to get ahead of the COVID-19 community outbreak.

"We have woken up to a very different South Australia today," South Australia Premier Steven Marshall said on Thursday.

In the country's strictest lockdown yet, all South Australians except for essential workers, must stay inside at home.

And they're not even allowed out for exercise. 

When the wide-ranging restrictions were announced yesterday, supermarkets and liquor stores quickly filled with frenzied shoppers.

"I've never ever seen it like this, and the announcement was only what 30 minutes ago?" A resident said on Wednesday.

"Yeah 12:30 we heard about it and we were out the door and basically here in a couple of minutes," another said.

There are now 23 positive cases linked to the 'Parafield cluster' -  and while there were no more reported today, 17 people are being treated as suspected cases. 

Stephen Mearns, a Kiwi living in Adelaide is an essential worker, and said the CBD is a ghost town. 

"I think the biggest thing is just the uncertainty on whether it will remain six days," he said.

"We do have a husky who is going to be going stir crazy not being able to be taken for a walk over the next few days, so just a bit of an adjustment."

An adjustment that South Australian authorities say will be critical if the state wants to get ahead of the latest outbreak.